Method of regulating the titer of a solution, device for controlling said regulation, and system comprising such a device

ABSTRACT

The invention concerns a system for regulating the titer of a solution, which consists in adding in the solution a predetermined amount of a product contained in the solution in a time interval, called addition time interval, proportional to the product of the time coefficient D of degradation of said product in solution and to the total volume Vt of the solution at the time of the addition. The invention also concerns a device for controlling the regulation of the titer of a solution, said solution containing a product, comprising means ( 10 ) for controlling injection of a predetermined amount of said product into said solution according to a time interval, called addition time interval, proportional to the product of the time coefficient D of degradation of said product and to the total volume Vt of the solution at the time of addition.

TECHNICAL FIELD AND PRIOR ART

The invention relates to the field of chemical regulation, in particular the chemical regulation of slurries or compounds of material in suspension and/or of various chemical products (acids, bases, organic compounds) in solution.

Such products are used, for example, in the semiconductor industry where they serve in the chemical-mechanical polishing of semiconductor wafers or substrates.

Some of these slurries or these suspensions use a compound whose concentration decreases over time, for example by decomposition by chemical reaction (this is the case with H₂O₂) or by evaporation (NH₄OH).

It is therefore necessary in this case to regulate the titre of chemical product(s) (H₂O₂, NH₄OH) of this slurry.

The current techniques for regulating slurries employ a buffer tank 4 and a mixing tank 2, as illustrated schematically in FIG. 1. The products leaving the buffer tank are then taken into a delivery system 8 and are used in operations such as the abovementioned polishing operations.

The operation of the tanks 2 and 4 may be described in the case of H₂O₂.

The tanks 2, 4 operate between a high level (Level_(max)) and a hysteresis level which triggers the filling.

They are regulated in terms of H₂O₂ titre (% wt). The filling of the buffer tank 4 takes place when the hysteresis level is reached, with slurry that comes from the mixing tank 2.

The slurry delivery system is composed of a continuous circulation loop, as described in U.S. Pat. No. 6 125 876, which prevents the slurry from stagnating in the network and makes it possible to regulate the pressure to the equipment by means of a pressure sensor. The feed and the return in this loop are at the base of the buffer tank 4.

The mixing tank 2 is fed with “pure” slurry and with hydrogen peroxide (for example 31% H₂O₂). It is regulated in terms of titre before each transfer of product into the buffer tank 4.

The hydrogen peroxide titre is regulated by provision of 31 wt % H₂O₂.

The titration operations carried out on the buffer tank 4 use a potentiometric titrator 7 or sometimes two titrators.

The titrator takes a measurement of the titre periodically (that can be paramaterized). Its operation can be described in conjunction with FIG. 2. This figure shows three titration levels, namely a high level (maximum value), a low level (minimum value) and a setpoint value to be reached.

If the titre is below the setpoint (Case 1 in FIG. 1), a readjustment is made by adding the lacking amount of H₂O₂.

Should the titre be above the setpoint (Cases 2 and 4 in FIG. 1), no regulating action is taken.

Should the titre be above the maximum value (Case 3 in FIG. 1), a second check is carried out. If this confirms that the titre is too high, an alarm is triggered. If the titre proves to be normal after the second check, no regulating action is taken.

Should the titre be below the minimum value (Case 5 in FIG. 1), a second check is carried out. If this confirms that the titre is too low, an alarm is triggered. If the titre proves to be normal after the second check, no regulating action is taken.

Triggering an alarm results in the delivery system 8, and therefore the production being stopped.

Moreover, each titrator employs, in particular, elements such as electrodes and capillaries.

The measurement taken furthermore depends on the titration reactants and on any drift of the electrodes or capillaries. There are therefore many sources of error.

Furthermore each titrator represents in general an overall cost of about 10% of the overall cost of the production plant on which it is mounted.

Each titrator is also a source of breakdowns and therefore entails substantial operating costs.

A problem that arises is to find a novel system of regulating the titrartion of suspensions, especially within the context of the fabrication of production units for semiconductor wafers or substrates, which is free of the abovementioned drawbacks.

SUMMARY OF THE INVENTION

The invention provides a method for regulating the titre of a solution, in which a predetermined amount of a product contained in the solution is added to the solution according to a time interval proportional to the product of the delayral degradation coefficient D of the said product in solution and the total volume Vt of the solution at the time of the addition.

This method depends only on the calculation of the addition interval, which depends only on the measurement of the total volume of the solution. This measurement may be performed in an analogue manner.

The method according to the invention entails a much lower cost that the method employing a titrator, and is also not a source of breakdowns, unlike known titrators. It does not employ electrodes that can drift and it does not depend on titration reactants either.

After each addition of product, the time interval before the next injection may be calculated.

Thus, it is possible, after a certain period of time less that the addition interval, to measure the total volume of the solution. If this volume has not varied, the same predetermined amount of product is again injected or added. If the total volume has decreased, a new addition time is calculated according to the same calculation rule.

The invention also relates to a device for controlling the regulation of the titre of a solution, this solution containing a product, comprising means for controlling the injection of a predetermined amount of the said product into the said solution according to a time interval, called the addition interval, proportional to the product of the delayral degradation coefficient D of the said product in solution and the total volume Vt of the solution at the time of the addition.

The invention also relates to a system for regulating the titre of a solution, comprising a device as above, and means for determining a fill volume in a container containing the said solution. These means for determining a fill volume may be analogue means.

Such a regulating system may furthermore include an electrode titration device.

The invention also relates to a system for producing a chemical solution, comprising:

-   -   a regulating system as above;     -   means for delivering the said solution.

According to the invention, a system for producing semiconductor substrates includes a unit for polishing the said substrates and a system for producing a chemical polishing solution as above.

BRIEF DESCRIPTION OF THE FIGURES

The features and advantages of the invention will become more clearly apparent on reading the description as follows of several embodiments given by way of non-limiting examples. The description refers to the appended figures in which:

FIG. 1 shows a known regulating system;

FIG. 2 shows various states of filling of a tank;

FIG. 3 shows a regulating system according to the invention;

FIG. 4 shows decomposition curves for a product in a tank; and

FIG. 5 shows a device for injecting a product, especially in a system according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 3 shows a diagram of a regulating system according to the invention. This diagram, like that in FIG. 1, relates to the regulation of slurries (or compounds of material in suspension and/or various chemical products in a solution) in a semiconductor wafer or substrate production unit. The references 2, 4, 6 and 8 denote elements identical or equivalent to those of FIG. 1.

Table 1 below summarizes the abbreviations used in the present description, illustrated (non-restrictingly) with a few numerical values in the right-hand column.

Indices:

-   -   i: initial     -   add: added     -   meas: measured     -   slur: slurry     -   m: slurry/hydrogen peroxide mixture     -   mix: mixing tank     -   targ: target or desired value

pure: undiluted TABLE 1 Unit Value Parameters Definition Values Type Example Deg_(buffer) Amount of H₂O₂ degradation % H₂O₂/day Measured 0.189% in the slurry in the value on H₂O₂/day buffer tank the curve Deg_(mix) Amount of degradation of % H₂O₂/day Measured 0.189% H₂O₂ in the slurry in the value on H₂O₂/day mixing tank the curve Diff_(mix) Maximum difference for the % H₂O₂ Calculation  0.06% mixing tank between the last H₂O₂ titre analysis and the new one K/K_(mix)/K_(buffer) Coefficient of addition of % H₂O₂ Calculation  0.16% the 100 ml dose of H₂O₂ in the slurry for a mixing tank/buffer tank M_(H) ₂ _(o) ₂ _(,add) Mass of H₂O₂ to be added to kg Calculation   523 kg the tank M_(slurry,i) Mass of slurry in the tank kg Measurement  1123 kg before analysis M_(added slurry) Mass of slurry to be added kg Calculation   523 kg to the tank M_(tank) Maximum weight of slurry kg Parameters  1360 kg in the tank Level_(max) Maximum permissible level % of Parameters   95% in the tank filling Level_(working) Permissible working level % of Parameters   90% in the tank filling Level_(hyst) Range of variation in the % of Parameters   35% mixing tank/buffer tank filling Level_(min) Minimum permissible level % of Parameters   60% in the tank filling Level_(tank) “Current” level in the % of Measurement   68% mixing tank filling Level_(slurry) Level of slurry to be % of Calculation   10% added to the tank filling Level_(H202) Level of H₂O₂ to be added % of Calculation    1% to the tank filling N_(buffer) Stirring power number in number Parameters −5_0 the buffer tank N_(mix) Stirring power number in number Parameters −5_0 the mixing tank N_(titration, mix) Successive titration number Parameters 1-4 number of the mixing tank during an off-spec analysis before a fault is triggered Slurry_(m) Mixing of on-spec H₂O₂ and slurry Amount_(fill) % Level in the tank % Measurement  65.5% Time_(inter-analysis) Time before the new day System    2 day analysis of the mixing value tank after an off-spec titre Time_(additions/analysis) Determination of the time minutes Parameters   40 min between the end of the H₂O₂ additions and the analysis of the in-tank H₂O₂ titre Time_(buffer inject) Time between each new minutes System   35 min Time_(mix inject) injection of H₂O₂ into the value tank for the doses added. Timelject_(mix) Time since last titration 0-21 System Existent of the mixing tank days value Titre_(H) ₂ ₀ ₂ _(,pure) Desired (target) H₂0₂ titre wt % Parameters  4.2% Titre_(H) ₂ ₀ ₂ _(,targ) in the tank Titre_(H) ₂ ₀ ₂ _(,i) H₂0₂ titre to be used for wt % Parameters   31% the additions Titre_(H) ₂ ₀ ₂ _(,meas) H₂0₂ titre measured in the wt % Parameters  4.18% tank Titre_(pure H) ₂ ₀ ₂ H202 titre used in pure form, undiluted Minimum value of the wt % Parameters  4.15% desired H₂0₂ titre in the tank Titre_(min) Maximum value of the wt % Parameters  4.25% desired H202 titre in the tank Titre_(max) Precise volume of the millilitres Parameters   104 ml 100 ml H₂O₂ injection dose V1 Precise volume of the millilitres Parameters   875 ml 900 ml H₂O₂ injection dose V2 Precise volume of the millilitres Parameters  9012 ml 9000 ml H₂O₂ injection dose V3 Volume of Slurry_(m) in the % fill System   78% buffer tank value V_(buffer) Volume of the tank − volume of slurry V_(total buffer) Vol_(H) ₂ ₀ ₂ _(,i) Volume of concentrated H₂O₂ litres Calculation   65 litres to be added to the mixing tank Vol_(added slurry) Volume of slurry to be litres Calculation   261 litres added to the mixing tank ρ_(H) ₂ ₀ ₂ _(i) Density of H₂O₂ to be used kg/m³ Fixed value 1.11 kg/m³ for the additions ρ_(slurry) Density of the slurry kg/m³ Fixed value 1.043 kg/m³ K_(mix) Theoretical degradation % H₂O₂/D Parameters new per day of the H₂O₂ titre 0-0.4 in the mixing tank for a full tank

The buffer tank 4 is regulated as follows.

An injection of a predetermined volume (for example, 100 ml) is programmed at a time interval that depends on several parameters:

-   -   1—on K, coefficient of addition of the 100 ml of H₂O₂ dose for         the slurry:     -   K depends on:         -   the maximum volume in the buffer tank,         -   the precise volume of the H₂O₂ dose to be added and in             principle, on the stirring rate in the tank;     -   2—on the volume in the tank in question at the time of the         addition, i.e. V_(total-buffer)=Vt_(buffer)×Factor_(fill);     -   3—on the daily H₂O₂ degradation coefficient Deg_(buffer) in the         tank.

As regards the buffer tank, the time between two injections is given by: Time_(inject buffer) =K×Deg_(buffer) ×V _(buffer).

A controller 10 (for example, a programmed micro-controller) carries out the calculation, after each H₂O₂ injection, of the delay before the next injection. This controller comprises means for storing the various data used for the calculation and a microprocessor that carries out the desired calculations and manages and controls the various product injections.

Moreover, a measurement of the volume in the tank 4 is made, for example by conventional analogue means.

After the calculated delay, the controller performs a test on the new measured volume in the tank:

-   -   if there is no change in level (for example within ±4%), the         predetermined dose is then injected;     -   if there is a decrease in level (product was consumed since the         last addition), the controller re-calculates the injection delay         according to the new volume. The time already elapsed is         subtracted from the new delay so as to determine at what moment         the new addition will be made; and     -   upon filling the buffer tank, the addition operation is         initialized at “time=O” and the calculation of the time is         repeated according to the new level (no addition at t=0).

In fact, K depends on the specifications of the tank (height, diameter, volume) and on the stirring rate, whereas the degradation coefficient Deg itself depends on K and on the volume ratio of energy dissipated in the slurry (in W/m³).

The coefficient K and the degradation curve for a given tank are determined in the following manner.

The H₂O₂ degradation measurements are made as a function of the level in the tank. A curve of the type of those illustrated in FIG. 4 is then obtained.

The method used is as follows:

-   -   fill the tank to 90% with a slurry mixture     -   whose H₂O₂ titre is known (about 4.2%);     -   wait 24 hours and then measure the titre again;     -   purge the tank in order to vary the level and reset the mixture         to the titre (about 4.2%);     -   wait 24 hours and then measure the titre again;     -   repeat several times in order to obtain enough points; and     -   deduce therefrom decomposition curve for the H₂O₂ in the tank as         a function of its fill level.

The coefficient K is the coefficient of the exponential function found. Thus, in FIG. 4, one curve has as coefficient K=0.1613 and the other K=0.0644.

The curve giving the variations in the degradation coefficient D as a function of the fill factor is identical or similar to that expressing the variations in the degradation coefficient D as a function of a stirring rate for a fixed level in the tank. This is because, in one case the energy (W) is varied and in the other case the volume (m³) is varied. However, these two variables are of the same order of magnitude. If both the stirring rate and the level in the tank are varied at the same time, a representation in the form of isolevels is obtained and therefore one with several curves. In all cases, these variables do not depend on the H₂O₂ dose.

In order to add a further safety factor to the system described above, it is also possible to add a measurement by a conventional titrator or an electrode titrator.

The H₂O₂ addition is then always made as described above, but regular analysis by the titrator allows the measurement to be validated.

The operation is then as below, the various cases being those in FIG. 2.

-   Case 1: should the titre be below the setpoint, re-adjustment as in     the mode of regulation by the titrator (already described above in     the introduction). -   Case 2: should the titre be above the setpoint, no action. -   Case 3: should the titre be above the maximum value, a second     measurement is taken:     -   if this confirms that the titre is too high, an alarm is         triggered, and additions are stopped;     -   if at the second measurement the titre appears normal, no action         is undertaken.

Case 4: should the titre be similar to the maximum value (for example greater than the maximum value −0.01%), a second measurement is taken:

-   -   if this confirms that the titre is too high, an alarm is         triggered and additions are stopped;     -   if at the second measurement the titre appears normal, no action         is undertaken.

-   Case 5: should the titre be below the minimum value, a second     measurement is taken:     -   if this confirms that the titre is too low, an alarm is         triggered and the titre is adjusted;     -   if at the second measurement the titre appears normal, no action         is undertaken.

The foregoing description relates to the buffer tank 4.

The mixing tank 2 is regulated in terms of H₂O₂ titre (wt %) before each filling of the buffer tank and in terms of fill (%) after each transfer to the buffer tank 4.

The filling of this tank 2 and its setting to the titre take place in the following manner.

First, a mixture is prepared. The level in the tank 2 is maintained between:

-   -   a level Level_(min)=Level_(max)−Level_(hyst) (F1) and     -   a level Level_(working)=Level_(max)×0.95 (F2),         where 0.95 is a safety factor allowing the H₂O₂ titre to be         adjusted without the high level in the mixing tank being         exceeded.

The level in the tank decreases as Slurry_(mix) is transferred from the mixing tank 2 to the buffer tank 4. The level is reset after each fill if the final level in the mixing tank 2 reaches the value Level_(min).

The product in the mixing tank 2 is prepared with Slurry_(p) (“pure” slurry with no H₂O₂) and 31 wt % hydrogen peroxide.

This preparation is carried out so as to obtain a level in the mixing tank such that: Level_(max)×0.95=(Level_(initial)+Level_(slurry)+Level_(H) ₂ _(O) ₂ )   (F3)

The H₂O₂ to be added by filling the mixing tank 2 is calculated using the following formula (F4): Titre_(H) ₂ _(O) ₂ =Vol_(H) ₂ _(O) ₂ _(,i)×ρ_(H) ₂ _(O) ₂ _(,i)×titre_(H) ₂ _(O) ₂ _(,i)/(Vol_(H) ₂ _(O) ₂ _(,i)×ρ_(H) ₂ _(O) ₂ _(,i)+Vol_(added slurry)×ρ_(slurry))

The following formula for calculating the hydrogen peroxide to be added to the mixing tank is then obtained: M _(H) ₂ O ₂ _(,add) =M _(slurry,i)×Titre_(H) ₂ _(O) ₂ _(,targ)/(Titre_(H) ₂ _(O) ₂ _(,i)−Titre_(H) ₂ _(O) ₂ _(,targ))   (F5).

In practice, the various filling steps are carried out in the following manner:

-   -   1) the line for filling the mixing tank with the slurry is         firstly rinsed (delay);     -   2) then the tank is filled with the slurry: M_(added slurry)         according to the formula (F6):         M _(slurry,add) =M         _(tank)×(Level_(max)×0.95−Level_(initial))×Titre_(H) ₂ _(O) ₂         _(,targ)/(Titre_(H) ₂ _(O) ₂ _(,i)−Titre_(H) ₂ _(O) ₂ _(targ))           (F6);     -   3) next, the line for filling the mixing tank with DIW is rinsed         (delay);     -   4) the valve for filling the mixing tank is then rinsed with DIW         (delay);     -   5) next, the tank is filled with H₂O₂ (M_(H) ₂ _(O) ₂ _(,add))         where:         M _(H) ₂ _(O) ₂ _(,add) =M         _(tank)×(Level_(max)0.95−Level_(initial)×Titre_(pure H) ₂ _(O) ₂         /Titre_(H) ₂ _(O) ₂ )   (F7);     -   6) waiting while the mixing tank homogenizes (waiting         time=Time_(additions/analysis));     -   7) next, the mixing tank is analysed and its titre obtained:         Titre_(H) ₂ _(O) ₂ _(meas)     -   if Titre_(min)≦Titre_(H) ₂ _(O) ₂ _(meas)≦Titre_(max),         validation of the mixing tank—the procedure passes to stage 10)     -   if Titre_(H) ₂ _(O) ₂ _(meas)≦Titre_(max):         -   carry out another analysis for confirmation             (N_(titration, mix)),         -   if confirmation, an alarm is triggered and a request for             operator intervention is generated,     -   if Titre_(H) ₂ _(O) ₂ _(meas)<Titre_(min), a titre is adjusted         and then the procedure passes to stage 8):         -   check that Titre_(H) ₂ _(O) ₂ _(,targ)−Titre_(H) ₂ _(O) ₂             _(,meas)<Diff_(mix) (where Diff_(mix) is the maximum             difference in the case of the mixing tank between the last             determination of the H₂O₂ titre and the new one),         -   carry out another determination for confirmation             (N_(titration, mix));     -   8) the titre is then adjusted, the adjustment steps being the         following:         -   calculation of the H₂O₂ volume to be added using formula             (F8),         -   H₂O₂ addition for adjustment (as a result of the decrease in             the H₂O₂ titre) and         -   waiting for homogenization of the mixing tank (waiting             time=Time_(additions/analysis));     -   9) the mixing tank is analysed in order to confirm that the         titre is within specification; and     -   10) there is then a wait for a demand to fill the buffer tank.

The titre of the tank 2 is regulated in the following manner. In fact, the same calculating method is used to calculate the mass of hydrogen peroxide to be added to the mixing tank 2 in order to regulate the titre: M _(H) ₂ _(O) ₂ _(,add) =M _(slurry,i)×(Titre_(H) ₂ _(O) ₂ _(,targ)−Titre_(H) ₂ _(O) ₂ _(,meas))/(Titre_(H) ₂ _(O) ₂ _(,i)−Titre_(H) ₂ _(O) ₂ _(,targ))   (F8)

The successive steps are then the following:

-   -   1) Analysis of the mixing tank. Hence the titre obtained:         Titre_(H) ₂ _(O) ₂ _(,targ)         -   if Titre_(min)≦Titre_(H) ₂ _(O) ₂ _(,meas)≦Titre_(max), then             validation of the mixing tank, and the procedure passes to             step 10)     -   if, Titre_(H) ₂ _(O) ₂ _(,meas)>Titre_(max):         -   carry out another analysis for confirmation             (N_(titration,mix))         -   if confirmation, alarm and request intervention by an             operator,     -   if Titre_(H) ₂ _(O) ₂ _(,meas <Titre) _(min), the titre is         adjusted and the procedure passes to step 8):         -   then check that Titre_(H) ₂ _(O) ₂ _(, targ)−Titre_(H) ₂             _(O) ₂ _(,meas)<Diff_(mix) (where Diff_(mix) is the maximum             difference for the mixing tank between the last             determination of the H₂O₂ titre and the new one),         -   carry out another analysis for confirmation             (N_(titration, mix));     -   2) adjustment of the titre:         -   calculation of the H₂O₂ volume to be added using formula             (F8),         -   H₂O₂ addition for adjustment (as a result of the decrease in             the H₂O₂ titre),         -   waiting for the mixing tank to homogenize (waiting             time=Time_(additions/analysis));     -   3) analysis of the mixing tank in order to confirm that the         titre is within specification; and     -   4) waiting for a request to fill the buffer tank.

The buffer tank 4 is, for its part, constantly regulated in terms of H₂O₂ titre (wt %) and in terms of filling (%).

The level in the tank is maintained between:

-   -   a level: Level_(min,i)=Level_(max)−Level_(hyst) (F1) and     -   a level: Level_(working)=Level_(max)×0.95 (F2) where 0.95 is a         safety factor that allows the H₂O₂ titre to be adjusted without         the high level being exceeded in the mixing tank.

The level in the tank 4 decreases as product is consumed by the equipment.

It is then filled with Slurry_(m) which comes from the mixing tank 2, as soon as its level goes below the level Level_(hyst).

The filling steps are carried out as follows:

-   -   1) request to fill the mixing tank 2;     -   2) —mixing tank 2 not ready: on standby—mixing tank 2 ready:         proceed to step 3);     -   3) rinsing of the line for filling the buffer tank with         Slurry_(m) and then filling of the buffer tank with Slurry_(m)         until the level Level_(max)×0.95;     -   4) rinsing of the line for filling the mixing tank with DIW         (delay).

The formula for regulating the titre in the buffer tank 4, making it possible to calculate the amount of hydrogen peroxide to be added, is the same as in the mixing tank: M _(H) ₂ _(O) ₂ _(,add) =M _(slurry,i)×(Titre_(H) ₂ _(O) ₂ _(,targ)−Titre_(H) ₂ _(O) ₂ _(,meas))/(Titre_(H) ₂ _(O) ₂ _(,i)−Titre_(H) ₂ _(O) ₂ _(,targ))   (F8).

The hydrogen peroxide is added to the buffer tank via metering tanks on the product return.

A valve system called a “block and bleed” system is used for adding hydrogen peroxide while preserving the tank from any in-line leaks which would add hydrogen peroxide to the buffer tank when filling the mixing tank with peroxide.

The titre is regulated using the method already explained above.

As regards the titration of the mixing tank 2, this takes place in the following manner. The permissible value with respect to the difference between two determinations carried out on the mixing tank depends on a parameter Deg_(mix) (H₂O₂ degradation coefficient).

The H₂O₂ titre degradation coefficient in the mixing tank 2 itself depends on the stirring in the tank and on the level in the tank.

This is because although the stirring rate in the tank is constant the energy dissipated per unit volume can vary. Consequently, the rate of degradation in the tank depends on its slurry level.

The degradation curve is therefore a power curve (typical of stirring phenomena).

It is therefore possible to estimate the H₂O₂ titre reduction in the tank between two determinations:

-   -   mixing tank difference in %=Diff_(mix)     -   mixing tank degradation in %/per day=Deg_(mix) where         Deg_(mix)=K_(mix)×Level_(mix tank);     -   time since last titration in days=time_(mix inject)         Diff_(mix)=Deg_(mix)×Time_(mix inject).

If a determination of the titre indicates that the titre is too low in the mixing tank 2 (Titre_(H) ₂ _(O) ₂ _(,targ)−Titre_(H) ₂ _(O) ₂ _(meas)<Diff_(mix)), the system triggers a titre readjustment by H₂O₂ addition.

If a determination indicates that the titre is too high in the mixing tank, the system triggers, after successive confirmation, a “mixing tank titre too high” alarm which disappears when the titre becomes normal again.

Another determination carried out on the tank is performed after a Time_(inter-analysis) which is calculated as follows: Time_(inter-analysis)=Diff_(mix)/Deg_(mix).

If there is a titration alarm:

During determination of the titre, if the value is such that Titre_(H) ₂ _(O) ₂ _(,targ)−Titre_(H) ₂ _(O) ₂ _(meas)>Diff_(mix), the system triggers (after N_(titration,mix) successive confirmations) an alarm and requests the intervention by an operator.

A titration error with regard to the mixing tank must not stop the system—it must only generate a minor defect (for H hours, a parameter that can be modified) and then a major defect after H hours if there has been no intervention by the operator.

The H₂O₂ additions are made using a system of containers which is filled with product, with venting to atmospheric pressure, followed by pressurization in order to fill one of the two tanks (buffer tank or mixing tank).

This arrangement illustrated in FIG. 5 consists of 3 successive containers 20, 22, 24 of volume known to within one millilitre:

-   -   a first container 20 of volume about V1=100 ml, known precisely;     -   a second container 22 of volume about V2=900 ml, known         precisely;     -   a third container 24 of volume about V3=9000 ml, known         precisely.

Example of use in the case of an 11.3 volume of H₂O₂:

-   -   filling of the containers;     -   draining down to the 10 000 millilitre level (V1+V2+V3);     -   filling of the containers;     -   draining down to the 1000 millilitre level (V1+V2);     -   filling of the containers;     -   draining down to the 100 millilitre level (V1);     -   filling of the containers;     -   draining down to the 100 millilitre level (V1);     -   filling of the containers; and     -   draining down to the 100 millilitre level (V1);

In fact, the volumes V1, V2 and V3 are not precise multiples of one hundred millilitres—the program of the controller 10 takes this into account when calculating the doses to be added.

In FIG. 5, the references 24 and 26 denote valves on a pressurization line and a venting line, respectively. The values 32 and 34 are valves for rapid addition and slow addition respectively, (via a calibrated orifice). The product is then sent into the tank 2 (valve 36) or the tank 4 (via valves 38 and 40) or else to a draining line via a valve 42.

The regulating method according to the invention applies especially to controlling the titre of a chemical solution for polishing semiconductor substrates.

A regulating system according to the invention therefore delivers a polishing product to delivery means. This product is then delivered to a substrate polishing unit. 

1-18. (canceled)
 19. A method for regulating the titration of a solution, comprising adding a predetermined amount of a product to the solution according to an addition interval, wherein said addition interval is a time interval proportional to the product of the time degradation coefficient D of said product in solution and the total volume Vt of the solution at the time of the addition.
 20. The method of claim 19, wherein said time interval before the next injection is calculated after each addition of said product.
 21. The method of claim 20, wherein said total volume Vt of the solution is measured after a certain period of time less than said addition interval.
 22. The method of claim 21, wherein a new addition time is calculated if the total volume has decreased.
 23. The method of claim 19, wherein said addition interval is K×D×Vt, wherein K is a coefficient which is a function of the stirring speed of said solution and the geometrical characteristics of the container containing said solution.
 24. The method of claim 19, in which the time degradation coefficient of said product in solution is measured beforehand according to the degree of filling of a container with said solution or the stirring rate in said container.
 25. The method of claim 19, further comprising determining the titration of the solution by an electrode titrator.
 26. The method of claim 25, wherein an alarm is triggered when the titration measured by said electrode titrator is below a predetermined minimum value or is above a predetermined maximum value.
 27. The method of claim 26, wherein at least two successive measurements are made by said electrode titrator when a measurement is below said maximum value before the alarm is triggered.
 28. The method of claim 19, wherein said solution is a solution for polishing semiconductor substrates.
 29. A process for polishing semiconductor substrates comprising: a) providing said semiconductor substrates; b) preparing a solution, wherein the method of regulating the titration of said solution comprises adding a predetermined amount of a product to the solution according to an addition interval, wherein said addition interval is a time interval proportional to the product of the time degradation coefficient D of said product in solution and the total volume Vt of the solution at the time of the addition; and c) polishing said semiconductor substrates with said solution.
 30. A device for controlling the regulation of the titration of a solution, comprising: a) a product; and b) a means for controlling the injection of a predetermined amount of said product into said solution according to an addition interval, wherein the addition interval is a time interval proportional to the product of the time degradation coefficient D of said product in solution and the total volume Vt of the solution at the time of the addition.
 31. The device of claim 30, further comprising a means for determining the time interval before the next injection after each addition of product.
 32. A system for regulating the titration of a solution, which comprises a device according to claim 30 and a means for determining a fill volume in a container containing said solution.
 33. The system of claim 32, wherein the means for determining said fill volume are analog means.
 34. The regulating system of claim 32, further comprising an electrode titration device.
 35. A system for producing a chemical solution, comprising: a) a system for regulating the titration of a solution, which comprises a device comprising: i) a product, and ii) a means for controlling the injection of a predetermined amount of said product into said solution according to an addition interval, wherein the addition interval is a time interval proportional to the product of the time degradation coefficient D of said product in solution and the total volume Vt of the solution at the time of the addition; and b) a means for delivering said solution.
 36. A system for producing semiconductor substrates, comprising: a) a unit for polishing said substrates, and b) a system for producing a chemical polishing solution, wherein the system for regulating the titration of said solution, which comprises a device comprising: i) a product, and ii) a means for controlling the injection of a predetermined amount of said product into said solution according to an addition interval, wherein the addition interval is a time interval proportional to the product of the time degradation coefficient D of said product in solution and the total volume Vt of the solution at the time of the addition. 